May 18, 1917] 



SCIENCE 



485 



protoplast, the remainder of whicli consists 

 largely of nitrogenous material, in the form 

 of albumen or albumen derivatives with an 

 unknown amount of lipin. The search for 

 material which might simulate the imbitional 

 behavior of growing tracts in plants begun by 

 the senior author resulted in finding that mix- 

 tures of agar with gelatine in which the last- 

 named substance was present in the smaller 

 proportion showed an enhanced capacity for 

 imbibition in distilled water and a reduced 

 swelling in weak acid and alkali as measured 

 in very thin plates by the auxograph.^ 



It is not certain, however, that the combina- 

 tion of amino-acids in gelatine is duplicated 

 in the plant and it was deemed important to 

 test the effects of simpler amino-aeid com- 

 pounds and of the more complex albumens on 

 the swelling of agar, as representing the basi- 

 cally important carbohydrates. Solutions of 

 the various mixtures were poured on glass 

 plates in layers about a centimeter thick and 

 3 by 5 cm. in area. Desiccation resulted in a 

 reduction of the length and width to about 

 half of the original. The thickness, however, 

 was reduced to one tenth or even as much as 

 to one thirtieth of the original, and having a 

 thickness of .1 mm. to .3 mm. in most cases. 

 The principal axis of deposition of material 

 was in the vertical and the swelling in this 

 direction would of course be correspondingly 

 in excess of that in the plane of the sections. 

 It is extremely unlikely that any of the col- 

 loidal masses of the cell are iso-radial as to 

 deposition or structure and the use of thin 

 plates seemed a feature which might increase 

 the similarity of behavior with that of the 

 plant. The strands, sheets or masses of mate- 

 rial in the cell are of course mostly thinner 

 than the plates used in the experiments, which 

 however, would affect speed of imbibition 

 more than total amount. 



Trios of. sections of sheets of the dried col- 

 loids 2 to 4 mm. by 3 to 6 mm. were placed in 

 the bottom of stender dishes or of heavy watch 

 glasses securely seated on iron cylinders. Tri- 



1 MacDougal, ' ' The Imbibitional Swelling of 

 Plants and Colloidal Mixtures," Science, N. S., 

 Vol. XLIV., pp. 502-505, 1916. 



angles of glass were placed on the sections, 

 and the vertical arms of auxographs were 

 rested in a socket in the center of the tri- 

 angles. Any change in thickness of the sec- 

 tions would be registered immediately. The 

 use of six instruments gave duplicate results 

 of the effects of water, acid and alkali, and 

 each record was an integration or average of 

 the swelling of three sections. 



The only albumen available when this plan 

 was put into operation was a commercial egg- 

 albumen, and this was first tested in mixtures 

 with large proportions of gelatine. The re- 

 sults of the swellings are as follows : 



Water HCl Ar/100 NaOH N/100 



Gelatine 

 (Average of 3 tests) 

 313.8% 825.5% 558.3% 



Gelatine 100 — Albumen 5 

 (Average of 5 tests) 

 283.4 611.7 482.2 



Gelatine 85 — Albumen 15 

 (Average of 5 tests) 

 408.6 827.8 673.0 



Gelatine 75 — Albumen S5 

 (Average of 3 tests) 

 378.3 569.7 508.7 



The albumen did not exert any important 

 influence on the swelling of the mixture until 

 it was present in proportions as great as 25 

 per cent. The action is not marked even in 

 this high proportion. ^Neither this nor any 

 other combination in which gelatine formed 

 the greater part displayed water relations at 

 all similar to those of the plant. 



ISText egg-albumen was added to agar and 

 agar-gelatine mixtures with results as below, 

 a further illustrative test being made of agar- 

 gelatine : 



Water HCl NilOO N.aOH 2V/100 



Agar 75 — Gelatine S5 

 (Average of 4 tests) 

 378.5% 427.3% 515.7% 



Agar 90 — -Albumen 10 

 (Average of 3 tests) 

 1,516.6 270.0 333.3 



(Average of 6 tests) 

 1,477.1 309.8 297.9 



Agar 90 — Gelatine 10 

 595.0 216.6 298.6 



The addition of ten per cent, of albumen to 

 agar notably reduced the capacity of agar for 

 swelling in acid and alkali, and appeared to 



